Journal of Women & Aging, 27:68–80, 2015 Copyright © Taylor & Francis Group, LLC ISSN: 0895-2841 print/1540-7322 online DOI: 10.1080/08952841.2014.928140
The Effect of Sensorimotor Training on the Postural Stability of Visually Impaired Women Over 50 Years of Age ´ ´ ZUZANNA MACKOWIAK, WIESLAW OSINSKI, and ARTUR SALAMON Department of Theory of Physical Education and Anthropomotorics, University School of Physical Education, Poznan, ´ Poland
Previous studies indicated that blind and visually impaired people are a group with greater risk of falls. Postmenopausal changes significantly decrease physical efficiency and impair the body’s mechanisms for maintaining postural stability. In addition, the frequency of falls among women is much higher than in men. The aim of this study was to analyze the effect of sensorimotor exercise on changes in postural stability of visually impaired women over 50 years of age. Visually impaired women from group E showed a lower level of postural stability measured with EO compared to the healthy women. After completing the exercise, a more pronounced improvement in the level of postural stability was observed in group E. KEYWORDS postural stability, sensorimotor training, visually impaired women, proprioception
INTRODUCTION Limited availability of visual information significantly impairs body balance, spatial orientation, and mobility, increasing the risk of dangerous falls and other causes of injuries. The incidence of falls in women is higher than in men (Melton, 2000). Postmenopausal changes have a significant impact on
Address correspondence to Zuzanna Ma´ckowiak, Department of Theory of Physical Education and Anthropomotoric, University School of Physical Education, ul. Krolowej Jadwigi 27/39, 61-871 Pozna´n, Poland. E-mail: [email protected] 68
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the enhanced rate of deterioration in body fitness and mechanisms responsible for maintaining postural stability (Kanis, Johnell, & Oden, 2000). A high level of sensory organization is necessary for maintaining the state of balance, which is considered one of the most important motor skills. Sensory integration plays a vital role in the development of motor skills, physical fitness, and spatial orientation (Akuthotaet & Nadler, 2004; Blomqvist & Rehn, 2007; Houglum, 2010). Methods of rehabilitation, associated with stimulating systems other than vision that control body posture, are postulated to play an important role in preventing age-related decrease in postural stability (Capicikova, Rocchi, Hlavacka, & Chiari, 2006; Sforza, Eid, & Ferrario, 2000). The somatosensory system, whose underlying mechanism is based upon the integration of information on reciprocal position of upper and lower limbs, is postulated to play a fundamental role in the process of compensating for visual impairment (Capicikova et al., 2006; Houglum, 2010; Sforza, Eid, Ferrario, Michielon, & Fragnito, 2003). Information from proprioceptors, particularly those located within the lower limb postural muscles, is particularly valuable in the context of maintaining normal body posture. The receptors sensitive to vibration, touch, pressure, and stretching play a particularly important role in this aspect (Capicikova et al., 2006; Rauschecker, 1995). The programs of sensorimotor training were revealed as an effective method of improving body balance and motor skills in humans. Sensorimotor exercise promotes the development of spatial organization and movement abilities, as well as a higher degree of utilization of sensory information, other than visual, in preventing anterior cruciate ligament injuries in female athletes (Mandelbaum et al., 2005). The results of previous studies suggest that demands placed upon the control systems during exercising on unstable ground improve both static and dynamic balance and consequently can reduce the risk of falling (Houglum, 2010). In this study, we analyzed the effect of sensorimotor training with Thera-Band stability trainers on changes in postural stability of visually impaired women over 50 years of age. We hypothesized that the application of sensorimotor training exerts a positive effect on the system of balance control, simultaneously effectively improving postural stability in visually impaired individuals.
METHODS Participants The study included a group of 30 visually impaired women (experimental group E) aged between 50 and 65 years (x = 58.9 ± 5.6 years). According to the International Classification of Functioning, Disability and Health (ICF)
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TABLE 1 Comparison of the Subjects Age and Morphological Characteristics Between the Two Groups (E—Experimental Group and C—Control Group) x ± SD
Age [years]
Height [m]
Weight [kg]
BMI (kg/cm2 )
E C F (1.58) (p)
58.90 ± 5.60 57.26 ± 4.94 1.50 (0.225)
1.63 ± 0.10 1.62 ± 0.06 0.02 (0.886)
78.23 ± 18.63 72.53 ± 15.07 1.70 (0.197)
29.39 ± 5.86 27.35 ± 4.85 2.16 (0.035)∗
∗
Significance at level P ≤ .05.
(World Health Organization, 1980), visually impaired women participating in our study represented two categories of visual deficit: high category of visual impairment with visual acuity of 20/200 and/or visual field limited to 20 degrees, or the medium category with visual acuity of 20/600 or lower and visual field of less than 5 degrees and able to recognize hand shapes. The participants of the study were recruited from the members of the Polish Association of the Blind. The control group (C) comprised 30 randomly selected women of similar age (50–65 years, x = 56.2 ± 4.9 years) without significant visual impairment. The age of the examined women was recorded; additionally, their basic somatic characteristics, i.e., body height, body weight, and body mass index (BMI; Table 1) were determined. Groups E and C did not differ significantly in terms of age, body height, and body mass. However, visually impaired women were characterized by significantly higher BMI (P ≤ .05).
Apparatus During examination, the signals illustrating the displacement of the center of gravity of the human body were recorded in the projection on a plane defined by X (right–left) and Y (anterior–superior) axes. Prior to the experiment, each of the participating women received detailed information about its objectives and protocols. Moreover, two preliminary tests were conducted in order to familiarize the subjects with the technique of measurement and eliminate potential confounders (anxiety, fear) during the valid trial. The measurements were taken under static conditions. The baseline position for the measurement was free standing on a posturographic platform with legs extended at the hip and knee joints. The feet were placed parallel to each other at the distance corresponding to the width of the hips, such that calcaneal tuberosity was positioned on the marked line on the platform. The participants were allowed to lift toes or heels off the platform but were instructed not to remove or displace the entire foot. Upper limbs were placed freely alongside the trunk. Each measurement was preceded by a 4-second determination of the center of pressure (COP) of the examined individual performed on the posturographic platform.
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Procedures The task of each examined subject pertained to maintaining as stable a posture as possible while standing on the posturographic platform. The 30second measurement began after the “start” command and ended at the “finish” command. The first test was conducted with eyes open (EO) and the second with eyes closed (EC). The following parameters were determined: AP—COP displacement in the anterior–posterior direction (distance between maximal and minimal position of COP in sagittal plane); ML—COP displacement in the mediolateral direction (distance between maximal and minimal position of COP in frontal plane); VAVG —total distance covered by COP divided by time duration (average velocity), and SACOP —sway area of COP limited with an ellipse of the 95th percentile (Stemplewski, Salamon, & Maciaszek, 2006). Subsequently, each participant performed an individual 16-minute set of exercises on unstable ground, simulated by two air-filled red Thera-Band stability trainers (Thera-Band, Poland). The participants from groups E and C performed identical exercises: toe-standing (30 repeats) and heel-standing (30 repeats), as well as one- and two-leg exercises: free standing and maximal voluntary sway of body in anterior–posterior and mediolateral directions. Each exercise was performed in accordance with Brugioni & Falkel’s (2004) and Powers, Buckley, Kaminski, Hubbard, and Ortiz’s (2004) protocol, both with EO and EC. Immediately after completing the exercise, the posturographic measurements were taken in accordance to the aforementioned procedure.
Statistical Analysis Statistical analysis of results was carried out with STATISTICA computer software (StatSoft Inc., Tulsa OK, USA). The levels of statistical significance were set at P ≤ .05 and P ≤ .01 for all the measurements. Normal distribution of analyzed variables was verified with the Shapiro-Wilk W-test. The significance of differences between mean values of posturographic parameters was examined with two-way ANOVA with repeated measures.
RESULTS The range of COP displacement in AP was analyzed separately for EO and EC (Figure 1). PRE represents the measurement taken prior to the exercise, while POST refers to that obtained immediately after exercise. Groups E and C did not differ significantly in terms of COP displacement in AP direction determined in EO condition (Figure 1). Group E, i.e., visually impaired women, was characterized by slightly higher values of AP both
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4,5
4,5
4,0
4,0
3,5
3,37 ± 1,27 3,25 ± 0,89
3,06 ± 1,22
3,0 2,5 2,0
2,92 ± 1,20
AP [cm]
AP [cm]
EO 5,0
3,5
* 3,98 ± 2,04 *
3,34 ± 1,19
3,28 ± 1,36
3,0 3,33 ± 1,25
2,5 PRE
POST
Group E
2,0
Group C
PRE
POST
Group E
Group C
FIGURE 1 Results of ANOVA, mean values, and standard deviations of COP displacement in anterior–posterior (AP) direction for the two groups (E—experimental group and C—control group) in two conditions (PRE pre-exercises condition, POST postexercises conditions). EO— eyes open and EC—eyes closed. ∗
Indicates a significant group x condition interaction (P ≤ .05).
TABLE 2 ANOVA Results for Interaction Effect and Between “Group” and “PRE–POST” Factor Effects of COP Displacement in Anterior–Posterior (AP) Direction in Measurements with EO (Eyes Open) and EC (Eyes Closed) Conditions AP
Interaction Effect(1.58) (P)
Factor “Group” F (1.58) (P)
Factor “PRE–POST” F (1.58) (P)
EO EC
0.01 (0.95)ns 4.17 (0.05)∗
1.98 (0.16)ns 0.44 (0.51)ns
0.49 (0.49)ns 3.45 (0.05)∗
∗
Significance at level P ≤ .05;
∗∗
significance at level P < .01.
prior to and after the exercise with stability trainers. In contrast, a significant increase in COP displacement by 0.95 ± 2.15 cm (P ≤ .05) was documented on POST measurement taken under EC condition in group C (Figure 1), while a slight reduction of this parameter was observed in group E. Further statistical analysis (Table 2) confirmed various effects of the implemented experimental factor on the range on COP displacement in AP direction. This was manifested by the statistically significant main effect of “PRE–POST” factor (F = 3.45, P ≤ .05), as well as by the interaction effect (F = 4.17, P ≤ .05). In both variants of measurement, higher values of COP displacement in the ML direction were documented in group E as compared to group C (Figure 2); this difference proved significant during the measurement under the EO condition (P ≤ .05). Furthermore, the statistically significant main effect of “Group” factor was confirmed (F = 6.65, P < .01; Table 3). In contrast, neither the significant main effect of “PRE–POST” factor (F = 0.21, P = .65) nor the interaction effect was observed (F = 0.11, P = .74). Consequently, the studied groups did not differ with regard to the extent
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The Effect of Sensorimotor Training on Postural Stability EO
EC 2,4
2,4
ML [cm]
2,0
*
* 1,87 ± 0,86
2,2 1,88 ± 0,99
1,8 1,6 1,4
1,48 ± 0,75 1,39 ± 0,59
1,8
1,80 ± 0,84
1,6 1,4
1,74 ± 1,01 1,65 ± 0,79
1,39 ± 0,64
1,2
1,2 1,0
2,0 ML [cm]
2,2
PRE Group E
POST Group C
1,0
PRE Group E
POST Group C
FIGURE 2 Results of ANOVA, mean values, and standard deviations of COP displacement in the mediolateral (ML) direction for the two groups (E—experimental group and C—control group) in two conditions (PRE—pre-exercises condition, POST—postexercises conditions). EO—eyes open and EC—eyes closed. ∗
Significant group and pre–post condition interaction (P ≤ .05).
TABLE 3 ANOVA Results for Interaction Effect and Between “Group” and “PRE–POST” Factor Effects of COP Displacement in Mediolateral (ML) Direction in Measurements with EO (Eyes Open) and EC (Eyes Closed) Conditions ML
Interaction Effect(1.58) (P)
Factor “Group” F(1.58) (P)
Factor “PRE–POST” F (1.58) (P)
EO EC
0.11 (0.74)ns 1.47 (0.23)ns
6.65 (0.01)∗∗ 2.20 (0.14)ns
0.21 (0.65)ns 0.65 (0.42)ns
∗
Significance at level P ≤ .05;
∗∗
significance at level P < .01.
of changes in the ML level during PRE and POST tests. No significant differences between the groups and between the time points of measurement were documented during measurement under the EC condition (Figure 2). However, the character of changes observed in the case of COP displacement in the ML direction was similar to that of the displacement in the AP direction. Analysis of changes of another posturographic parameter, i.e., VAVG determined under EO conditions (Figure 3), revealed a significant increase after completing the exercise on stability trainers by 0.13 ± 0.36 cm/s (P ≤ .05) in group E, i.e., visually impaired women, and by 0.17 ± 0.26cm/s (P < .01) in group C. Furthermore, on both measurements the value of COP VAVG was higher in group E than in group C. During the measurement taken under EC conditions (Figure 3), in both groups the baseline values of this parameter were higher than during the test under EO conditions, suggesting a significant effect of visual information on VAVG. Additionally, a significant increase (P ≤ .05) in this parameter was documented on the POST test in group C.
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Z. Ma´ckowiak et al. EO
2,4
2,4
2,2
2,2
2,0 1,8 1,6 1,4 1,2
* 1,57 ± 0,37
* *
1,70 ± 0,41 1,51 ± 0,34
*
1,85 ± 0,60 *
2,0 1,8 1,71 ± 0,71 1,6 1,65 ± 0,49
2,19 ± 1,34
1,4
1,34 ± 0,25 PRE Group E
EC
2,6
VAVG [cm/s]
VAVG [cm/s]
2,6
POST Group C
1,2
PRE Group E
POST Group C
FIGURE 3 Results of ANOVA, mean values, and standard deviations of COP velocity (VAVG ) for the two groups (E—experimental group and C—control group) in two conditions (PRE—preexercises condition, POST—postexercises conditions). EO—eyes open and EC—eyes closed. ∗
Significant group and pre–post condition interaction (P ≤ .05).
TABLE 4 ANOVA Results for Interaction Effect and Between “Group” and “PRE–POST” Factor Effects COP Average Velocity (VAVG ) in Measurements with EO (Eyes Open) and EC (Eyes Closed) Conditions VAVG
Interaction Effect(1.58) (P)
Factor “Group” F (1.58) (P)
Factor “PRE–POST” F (1.58) (P)
EO EC
0.20 (0.66)ns 2.81 (0.10)ns
6.91 (0.01)∗∗ 0.59 (0.45)ns
14.06 (0.01)∗∗ 8.40 (0.01)∗∗
∗
Significance at level P ≤ .05;
∗∗
significance at level P < .01.
Detailed analysis of measurements taken under EO conditions, the results of which are presented in Table 4, confirmed the significant main effect of “Group” factor (F = 6.91, P < .01), as well as the main effect of “PRE–POST factor (F = 14.06, P < .01). In contrast, neither the significant interaction effect (F = 0.20, P = .66) nor significant differences between groups E and C (F = 0.59, P = .45) were observed under EC conditions. However, the significant main effect of “PRE–POST” (F = 8.40, P < .01) was documented. Consequently, there was a statistically significant difference between measurements taken prior to and after sensorimotor exercise. Statistical analysis of SACOP under EO conditions (Figure 4) revealed that group E, i.e., visually impaired women, was characterized by higher values of this parameter as compared to group C (P ≤ .05), both on measurement taken prior to (PRE) and after (POST) completing the exercise on stability trainers. In contrast, during the measurement taken under the EC condition (Figure 4), a slight decrease in SACOP was observed in group E, whereas the significant increase in this parameter (P ≤ .05), by 1.32 ± 3.38 cm2 , was documented in group C. This direction of changes was analogous, as in the case of previously discussed parameters; thus, confirming the role of visual and proprioceptive factors in defining the level of body balance.
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The Effect of Sensorimotor Training on Postural Stability EO
5,0
*
4,0 3,5 3,0
3,38 ± 2,69 3,11 ± 1,99
2,5 2,0
4,5
*
2,33 ± 1,69 2,05 ± 1,32
4,0 3,5 3,0 2,5 2,0
3,55 ± 3,22 3,22 ± 2,66
3,01 ± 2,24 *
2,23 ± 1,55
1,5
1,5 1,0
SACOP [cm2]
SACOP [cm2]
4,5
EC
5,0
PRE
POST
1,0
PRE
POST
Group E
Group C
Group E
Group C
FIGURE 4 Results of ANOVA, mean values, and standard deviations of COP sway area (SACOP ) for the two groups (E—experimental group and C—control group) in two conditions (PRE—pre-exercises condition, POST—postexercises conditions). EO (eyes open) and EC (eyes closed). ∗
A significant group and pre–post condition interaction (P ≤ .05).
TABLE 5 ANOVA Results for Interaction Effect and Between “Group” and “PRE–POST” Factor Effects of COP Sway Area (SACOP ) in Measurements with EO (Eyes Open) and EC (Eyes Closed) Conditions SACOP EO EC ∗
Interaction Effect(1.58) (P)
Factor “Group” F(1.58) (P)
Factor “PRE-POST” F(1.58) (P)
0.01 (0.99)ns 3.44 (0.07)ns
6.39 (0.01)∗∗ 0.20 (0.65)ns
0.93 (0.34)ns 1.84 (0.18)ns
Significance at level P ≤ .05;
∗∗
significance at level P < 0. 1.
Furthermore, the statistically significant main effect of “Group” factor (F = 6.39, P < .01) on measurement taken with eyes open was documented (Table 5). The remaining changes in postural parameters proved statistically nonsignificant.
DISCUSSION AND CONCLUSION The aim of this study was to analyze the effect of sensorimotor training on the postural stability of visually impaired women over 50 years of age. We analyzed the changes that resulted from short-term exposure to destabilizing factors associated with sensorimotor exercise with Thera-Band stability trainers. The study aimed at enhancing the understanding of the process of controlling and maintaining stable posture through a detailed analysis of the determinants of postural stability. Our study sought to elucidate the relationship between postural stability, visual control, and the capacity of the proprioceptive system of the lower limbs. Perhaps understanding the complexity of the mechanisms underlying this process may prove helpful in
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improving the quality of life and promoting reduced falling risk in a group of individuals with visual impairment. Measurements taken with a posturographic system enabled us to analyze the ranges of COP displacement. It is widely believed that the higher range of COP displacement during free standing manifests a reduced level of stability (Judge, Lindsey, Underwood, & Winsemius, 1993; Lord, McLean, & Stathers, 1992). Moreover, the relationship between stable posture and age must be emphasized. It was revealed that progressive aging is associated with degenerative changes within various components of the system of balance control (Lord & Menz, 2000). Our study revealed that in both groups the exercise with stability trainers was reflected by a slight increase in AP, ML, VAVG , and SACOP values determined under static conditions with eyes open. According to Winter (1995), the increase in these parameters can be associated with an independent control of the range of swaying in the sagittal and horizontal plane. VAVG was the only parameter with significant differences between PRE and POST measurements in both groups (E and C). These findings suggest that sensorimotor training has an influence on decreasing postural stability. Detailed analysis conducted in group E revealed markedly higher postexercise values of such posturographic parameters as ML, VAVG , and SACOP . According to Mitchell, Collins, Luca, Burrows, and Lipsitz (1995), increased range of sway in the ML plane is associated with the increased risk of loss of balance and predisposes to falling. An increase in the aforementioned parameters, observed in visually impaired women as compared to the controls, can result from visual deficits. ´ Previous studies (Stemplewski, Maciaszek, Salamon, Tomczak, & Osinski, 2012) revealed that in static examination under EO conditions older individuals are characterized by lower values of posturographic parameters and thus seemingly better postural stability than younger subjects. This paradoxical phenomenon of increased values of COP parameters observed in our study could result from activation of compensatory mechanisms and hence suggest improved body balance in group E participants. Numerous previous studies documented that blind individuals are characterized by a lower level of postural stability, manifested by increased area of COP swaying in coronal and sagittal planes (Blomqvist & Rehn, 2007; Easton, Greene, Dizio, & Lackner, 1998; Schmid, Nardone, De Nunzio, Schmid, & Schieppati, 2007; Sforza et al., 2000). According to Rauschecker (1995) and Schmid et al. (2007), greater COP sways result from the lack of interaction between visual stimuli and motor behaviors. Our findings led us to the conclusion that during the static examination with eyes opened, the experimental group of visually impaired women exhibited a larger range of maximal COP displacement than the control group of women without visual dysfunction; this is reflected by a higher level of postural instability. Vision has the strongest impact on the range of anterior–posterior sway, and the deprivation of visual information is reflected by marked disorders
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of balance. Under such conditions, an immediate increase in the range of COP swaying occurs in individuals without visual impairment (Schieppati, Tacchini, Nardone, Tarantola, & Corna, 1999; Schmid et al., 2007; Sforza et al., 2000). Decreased values of AP, ML, and SACOP were observed during the closed eye measurement in group E; these findings should be interpreted as an increase in postural stability. The application of sensorimotor training was reflected by the activation of compensatory processes in the other systems of balance control. The deprivation of visual stimulation, associated with closing the eyes, resulted in the improvement of postural stability along with the decreased values of baseline characteristics. After completing sensorimotor exercises, a decrease in the amplitude of COP swaying in AP and ML planes, as well as in SACOP, was observed in visually impaired women. Furthermore, after completing the exercise on unstable ground, the values of COP sway in both planes documented in the group of visually impaired women were markedly lower than in the individuals without visual impairment. A reduction in postural stability was documented in the control group C as manifested by considerable increase in all studied parameters: AP, ML, VAVG , and SACOP . As a result of sensorimotor training, group E, composed of visually impaired women, showed a lower range of maximal COP displacement and higher level of postural stability during closed-eye measurement as compared to women without visual dysfunction. Moreover, this study revealed a different effect of visual information on the level of postural stability during measurements taken with open and closed eyes. In the case of visually impaired women, abolishing visual stimulation and implementing exercising on unstable ground was reflected by a higher level of postural stability and compensation of negative influence of visual impairment resulting from extremely effective involvement of other senses. Detailed analysis revealed reduced swaying in the horizontal plane during closed-eye measurement in the control group. These findings can be explained by the fact that identifying lateral movement of the body is easier for the sensimotor system than for the visual system and vestibular organ (Day, Streiger, Thompson, & Marsden, 1993). It is probably the sensorimotor system that is mostly responsible for compensatory function in visually impaired individuals (Capicikova et al., 2006; Sforza et al., 2000). Gravelle et al. (2002) and Collins et al. (2003) observed that greater sways lead to more intense perception of information from the sensorimotor system, consequently improving body stability. Häkkinen et al. (2006) expressed a similar opinion and suggested that to maintain stable posture blind individuals rely on the sensorimotor system to a greater extent than healthy people, who use visual information for this purpose. Patel et al. (2008) highlighted the changes in postural stability induced by visual and sensorimotor destabilizing factors. Our study, involving static measurement, enabled us to conclude that exercise on unstable ground improves postural stability under the open-eyes condition of women without visual dysfunction to a
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greater extent than in those with visual impairment. Previously, other authors (Hosseinimer & Norastech 2010; M˛etel, 2003) postulated the implementation of sensorimotor training programs, suggesting that they can significantly improve both static and dynamic balance of the body. Our findings indicate that women with visual dysfunction can be characterized by varying characteristics of postural stability. Additionally, we confirmed our initial hypothesis according to which the experimental factor, namely sensorimotor training, has a positive influence on analyzed parameters of postural stability, being an effective method of improving postural stability in visually impaired women over 50 years of age. The results of our study can be an important source of information during the planning of compensatory strategies. It should be remembered, however, that our results originate solely from measurements taken under laboratory conditions. In particular, we did not analyze the long-term effect of such an approach within the entire framework of the rehabilitation process of individuals with visual dysfunction, or from the point of view of reducing the risk of falls under natural conditions.
ACKNOWLEDGMENTS The research was conducted by the permission of the Institutional Review Board at Poznan University of Medical Sciences, 10 Fredry Str., 61701 Poznan´ , Poland, number 305/11 from June 16, 2011.
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Rauschecker, J. P. (1995). Compensatory plasticity and sensory substitution in the cerebral cortex. Trends in Neurosciences, 18, 36–43. doi:10.1016/0166-2236(95)93948-W Schieppati, M., Tacchini, E., Nardone, A., Tarantola, J., & Corna, S. (1999). Subjective perception of body sway. Journal of Neurology, Neurosurgery and Psychiatry, 66, 313–322. doi:10.1136/jnnp.66.3.313 Schmid, M., Nardone, A., De Nunzio, A. M., Schmid, M., & Schieppati, M. (2007). Equilibrium during static and dynamic tasks in blind subjects: No evidence of cross-modal plasticity. Brain, 130, 2097–2107. doi:10.1093/brain/awm157 Sforza, C., Eid, L., & Ferrario, V. (2000). Sensorial afferents and center of foot pressure in blind and sighted adults. Journal of Visual Impairment and Blindness, 94(2), 97–107. Sforza, C., Eid, L., Ferrario, V., Michielon, G., & Fragnito, N. (2003). Sensorial afferents, expectations, and craniocervical postural relations in adults who are blind and sighted. Journal of Visual Impairment and Blindness, 97(1), 17–27. Stemplewski, R., Maciaszek, J., Salamon, A., Tomczak, M., & Osi´nski, W. (2012). Effect of moderate physical exercise on postural control among 65–74 years old men. Archives of Gerontology and Geriatrics, 54(3), 279–283. doi:10.1016/ j.archger.2012.02.012 Stemplewski, R., Salamon, A., & Maciaszek, J. (2006). Static body balance posturographic values in medio-lateral and anterior-posterior directions in conditions of unstable base of support in men older than 70 years. Studies in Physical Culture and Tourism Supplement, 13, 85–87. Winter, D. A. (1995). Human balance and posture control during standing and walking. Gait and Posture, 3, 193–214. doi:10.1016/0966-6362(96)82849-9 World Health Organization (WHO). (1980). International Classification of Functioning, Disability and Health (ICF). A manual of classification relating to the consequences of disease. Geneva, Switzerland: World Health Organization. Retrieved from http://www.who.int/classifications/icf/en/
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The Effect of Sensorimotor Training on the Postural Stability of Visually Impaired Women Over 50 Years of Age ´ ´ ZUZANNA MACKOWIAK, WIESLAW OSINSKI, and ARTUR SALAMON Department of Theory of Physical Education and Anthropomotorics, University School of Physical Education, Poznan, ´ Poland
Previous studies indicated that blind and visually impaired people are a group with greater risk of falls. Postmenopausal changes significantly decrease physical efficiency and impair the body’s mechanisms for maintaining postural stability. In addition, the frequency of falls among women is much higher than in men. The aim of this study was to analyze the effect of sensorimotor exercise on changes in postural stability of visually impaired women over 50 years of age. Visually impaired women from group E showed a lower level of postural stability measured with EO compared to the healthy women. After completing the exercise, a more pronounced improvement in the level of postural stability was observed in group E. KEYWORDS postural stability, sensorimotor training, visually impaired women, proprioception
INTRODUCTION Limited availability of visual information significantly impairs body balance, spatial orientation, and mobility, increasing the risk of dangerous falls and other causes of injuries. The incidence of falls in women is higher than in men (Melton, 2000). Postmenopausal changes have a significant impact on
Address correspondence to Zuzanna Ma´ckowiak, Department of Theory of Physical Education and Anthropomotoric, University School of Physical Education, ul. Krolowej Jadwigi 27/39, 61-871 Pozna´n, Poland. E-mail: [email protected] 68
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the enhanced rate of deterioration in body fitness and mechanisms responsible for maintaining postural stability (Kanis, Johnell, & Oden, 2000). A high level of sensory organization is necessary for maintaining the state of balance, which is considered one of the most important motor skills. Sensory integration plays a vital role in the development of motor skills, physical fitness, and spatial orientation (Akuthotaet & Nadler, 2004; Blomqvist & Rehn, 2007; Houglum, 2010). Methods of rehabilitation, associated with stimulating systems other than vision that control body posture, are postulated to play an important role in preventing age-related decrease in postural stability (Capicikova, Rocchi, Hlavacka, & Chiari, 2006; Sforza, Eid, & Ferrario, 2000). The somatosensory system, whose underlying mechanism is based upon the integration of information on reciprocal position of upper and lower limbs, is postulated to play a fundamental role in the process of compensating for visual impairment (Capicikova et al., 2006; Houglum, 2010; Sforza, Eid, Ferrario, Michielon, & Fragnito, 2003). Information from proprioceptors, particularly those located within the lower limb postural muscles, is particularly valuable in the context of maintaining normal body posture. The receptors sensitive to vibration, touch, pressure, and stretching play a particularly important role in this aspect (Capicikova et al., 2006; Rauschecker, 1995). The programs of sensorimotor training were revealed as an effective method of improving body balance and motor skills in humans. Sensorimotor exercise promotes the development of spatial organization and movement abilities, as well as a higher degree of utilization of sensory information, other than visual, in preventing anterior cruciate ligament injuries in female athletes (Mandelbaum et al., 2005). The results of previous studies suggest that demands placed upon the control systems during exercising on unstable ground improve both static and dynamic balance and consequently can reduce the risk of falling (Houglum, 2010). In this study, we analyzed the effect of sensorimotor training with Thera-Band stability trainers on changes in postural stability of visually impaired women over 50 years of age. We hypothesized that the application of sensorimotor training exerts a positive effect on the system of balance control, simultaneously effectively improving postural stability in visually impaired individuals.
METHODS Participants The study included a group of 30 visually impaired women (experimental group E) aged between 50 and 65 years (x = 58.9 ± 5.6 years). According to the International Classification of Functioning, Disability and Health (ICF)
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TABLE 1 Comparison of the Subjects Age and Morphological Characteristics Between the Two Groups (E—Experimental Group and C—Control Group) x ± SD
Age [years]
Height [m]
Weight [kg]
BMI (kg/cm2 )
E C F (1.58) (p)
58.90 ± 5.60 57.26 ± 4.94 1.50 (0.225)
1.63 ± 0.10 1.62 ± 0.06 0.02 (0.886)
78.23 ± 18.63 72.53 ± 15.07 1.70 (0.197)
29.39 ± 5.86 27.35 ± 4.85 2.16 (0.035)∗
∗
Significance at level P ≤ .05.
(World Health Organization, 1980), visually impaired women participating in our study represented two categories of visual deficit: high category of visual impairment with visual acuity of 20/200 and/or visual field limited to 20 degrees, or the medium category with visual acuity of 20/600 or lower and visual field of less than 5 degrees and able to recognize hand shapes. The participants of the study were recruited from the members of the Polish Association of the Blind. The control group (C) comprised 30 randomly selected women of similar age (50–65 years, x = 56.2 ± 4.9 years) without significant visual impairment. The age of the examined women was recorded; additionally, their basic somatic characteristics, i.e., body height, body weight, and body mass index (BMI; Table 1) were determined. Groups E and C did not differ significantly in terms of age, body height, and body mass. However, visually impaired women were characterized by significantly higher BMI (P ≤ .05).
Apparatus During examination, the signals illustrating the displacement of the center of gravity of the human body were recorded in the projection on a plane defined by X (right–left) and Y (anterior–superior) axes. Prior to the experiment, each of the participating women received detailed information about its objectives and protocols. Moreover, two preliminary tests were conducted in order to familiarize the subjects with the technique of measurement and eliminate potential confounders (anxiety, fear) during the valid trial. The measurements were taken under static conditions. The baseline position for the measurement was free standing on a posturographic platform with legs extended at the hip and knee joints. The feet were placed parallel to each other at the distance corresponding to the width of the hips, such that calcaneal tuberosity was positioned on the marked line on the platform. The participants were allowed to lift toes or heels off the platform but were instructed not to remove or displace the entire foot. Upper limbs were placed freely alongside the trunk. Each measurement was preceded by a 4-second determination of the center of pressure (COP) of the examined individual performed on the posturographic platform.
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Procedures The task of each examined subject pertained to maintaining as stable a posture as possible while standing on the posturographic platform. The 30second measurement began after the “start” command and ended at the “finish” command. The first test was conducted with eyes open (EO) and the second with eyes closed (EC). The following parameters were determined: AP—COP displacement in the anterior–posterior direction (distance between maximal and minimal position of COP in sagittal plane); ML—COP displacement in the mediolateral direction (distance between maximal and minimal position of COP in frontal plane); VAVG —total distance covered by COP divided by time duration (average velocity), and SACOP —sway area of COP limited with an ellipse of the 95th percentile (Stemplewski, Salamon, & Maciaszek, 2006). Subsequently, each participant performed an individual 16-minute set of exercises on unstable ground, simulated by two air-filled red Thera-Band stability trainers (Thera-Band, Poland). The participants from groups E and C performed identical exercises: toe-standing (30 repeats) and heel-standing (30 repeats), as well as one- and two-leg exercises: free standing and maximal voluntary sway of body in anterior–posterior and mediolateral directions. Each exercise was performed in accordance with Brugioni & Falkel’s (2004) and Powers, Buckley, Kaminski, Hubbard, and Ortiz’s (2004) protocol, both with EO and EC. Immediately after completing the exercise, the posturographic measurements were taken in accordance to the aforementioned procedure.
Statistical Analysis Statistical analysis of results was carried out with STATISTICA computer software (StatSoft Inc., Tulsa OK, USA). The levels of statistical significance were set at P ≤ .05 and P ≤ .01 for all the measurements. Normal distribution of analyzed variables was verified with the Shapiro-Wilk W-test. The significance of differences between mean values of posturographic parameters was examined with two-way ANOVA with repeated measures.
RESULTS The range of COP displacement in AP was analyzed separately for EO and EC (Figure 1). PRE represents the measurement taken prior to the exercise, while POST refers to that obtained immediately after exercise. Groups E and C did not differ significantly in terms of COP displacement in AP direction determined in EO condition (Figure 1). Group E, i.e., visually impaired women, was characterized by slightly higher values of AP both
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Z. Ma´ckowiak et al. EC 5,0
4,5
4,5
4,0
4,0
3,5
3,37 ± 1,27 3,25 ± 0,89
3,06 ± 1,22
3,0 2,5 2,0
2,92 ± 1,20
AP [cm]
AP [cm]
EO 5,0
3,5
* 3,98 ± 2,04 *
3,34 ± 1,19
3,28 ± 1,36
3,0 3,33 ± 1,25
2,5 PRE
POST
Group E
2,0
Group C
PRE
POST
Group E
Group C
FIGURE 1 Results of ANOVA, mean values, and standard deviations of COP displacement in anterior–posterior (AP) direction for the two groups (E—experimental group and C—control group) in two conditions (PRE pre-exercises condition, POST postexercises conditions). EO— eyes open and EC—eyes closed. ∗
Indicates a significant group x condition interaction (P ≤ .05).
TABLE 2 ANOVA Results for Interaction Effect and Between “Group” and “PRE–POST” Factor Effects of COP Displacement in Anterior–Posterior (AP) Direction in Measurements with EO (Eyes Open) and EC (Eyes Closed) Conditions AP
Interaction Effect(1.58) (P)
Factor “Group” F (1.58) (P)
Factor “PRE–POST” F (1.58) (P)
EO EC
0.01 (0.95)ns 4.17 (0.05)∗
1.98 (0.16)ns 0.44 (0.51)ns
0.49 (0.49)ns 3.45 (0.05)∗
∗
Significance at level P ≤ .05;
∗∗
significance at level P < .01.
prior to and after the exercise with stability trainers. In contrast, a significant increase in COP displacement by 0.95 ± 2.15 cm (P ≤ .05) was documented on POST measurement taken under EC condition in group C (Figure 1), while a slight reduction of this parameter was observed in group E. Further statistical analysis (Table 2) confirmed various effects of the implemented experimental factor on the range on COP displacement in AP direction. This was manifested by the statistically significant main effect of “PRE–POST” factor (F = 3.45, P ≤ .05), as well as by the interaction effect (F = 4.17, P ≤ .05). In both variants of measurement, higher values of COP displacement in the ML direction were documented in group E as compared to group C (Figure 2); this difference proved significant during the measurement under the EO condition (P ≤ .05). Furthermore, the statistically significant main effect of “Group” factor was confirmed (F = 6.65, P < .01; Table 3). In contrast, neither the significant main effect of “PRE–POST” factor (F = 0.21, P = .65) nor the interaction effect was observed (F = 0.11, P = .74). Consequently, the studied groups did not differ with regard to the extent
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The Effect of Sensorimotor Training on Postural Stability EO
EC 2,4
2,4
ML [cm]
2,0
*
* 1,87 ± 0,86
2,2 1,88 ± 0,99
1,8 1,6 1,4
1,48 ± 0,75 1,39 ± 0,59
1,8
1,80 ± 0,84
1,6 1,4
1,74 ± 1,01 1,65 ± 0,79
1,39 ± 0,64
1,2
1,2 1,0
2,0 ML [cm]
2,2
PRE Group E
POST Group C
1,0
PRE Group E
POST Group C
FIGURE 2 Results of ANOVA, mean values, and standard deviations of COP displacement in the mediolateral (ML) direction for the two groups (E—experimental group and C—control group) in two conditions (PRE—pre-exercises condition, POST—postexercises conditions). EO—eyes open and EC—eyes closed. ∗
Significant group and pre–post condition interaction (P ≤ .05).
TABLE 3 ANOVA Results for Interaction Effect and Between “Group” and “PRE–POST” Factor Effects of COP Displacement in Mediolateral (ML) Direction in Measurements with EO (Eyes Open) and EC (Eyes Closed) Conditions ML
Interaction Effect(1.58) (P)
Factor “Group” F(1.58) (P)
Factor “PRE–POST” F (1.58) (P)
EO EC
0.11 (0.74)ns 1.47 (0.23)ns
6.65 (0.01)∗∗ 2.20 (0.14)ns
0.21 (0.65)ns 0.65 (0.42)ns
∗
Significance at level P ≤ .05;
∗∗
significance at level P < .01.
of changes in the ML level during PRE and POST tests. No significant differences between the groups and between the time points of measurement were documented during measurement under the EC condition (Figure 2). However, the character of changes observed in the case of COP displacement in the ML direction was similar to that of the displacement in the AP direction. Analysis of changes of another posturographic parameter, i.e., VAVG determined under EO conditions (Figure 3), revealed a significant increase after completing the exercise on stability trainers by 0.13 ± 0.36 cm/s (P ≤ .05) in group E, i.e., visually impaired women, and by 0.17 ± 0.26cm/s (P < .01) in group C. Furthermore, on both measurements the value of COP VAVG was higher in group E than in group C. During the measurement taken under EC conditions (Figure 3), in both groups the baseline values of this parameter were higher than during the test under EO conditions, suggesting a significant effect of visual information on VAVG. Additionally, a significant increase (P ≤ .05) in this parameter was documented on the POST test in group C.
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Z. Ma´ckowiak et al. EO
2,4
2,4
2,2
2,2
2,0 1,8 1,6 1,4 1,2
* 1,57 ± 0,37
* *
1,70 ± 0,41 1,51 ± 0,34
*
1,85 ± 0,60 *
2,0 1,8 1,71 ± 0,71 1,6 1,65 ± 0,49
2,19 ± 1,34
1,4
1,34 ± 0,25 PRE Group E
EC
2,6
VAVG [cm/s]
VAVG [cm/s]
2,6
POST Group C
1,2
PRE Group E
POST Group C
FIGURE 3 Results of ANOVA, mean values, and standard deviations of COP velocity (VAVG ) for the two groups (E—experimental group and C—control group) in two conditions (PRE—preexercises condition, POST—postexercises conditions). EO—eyes open and EC—eyes closed. ∗
Significant group and pre–post condition interaction (P ≤ .05).
TABLE 4 ANOVA Results for Interaction Effect and Between “Group” and “PRE–POST” Factor Effects COP Average Velocity (VAVG ) in Measurements with EO (Eyes Open) and EC (Eyes Closed) Conditions VAVG
Interaction Effect(1.58) (P)
Factor “Group” F (1.58) (P)
Factor “PRE–POST” F (1.58) (P)
EO EC
0.20 (0.66)ns 2.81 (0.10)ns
6.91 (0.01)∗∗ 0.59 (0.45)ns
14.06 (0.01)∗∗ 8.40 (0.01)∗∗
∗
Significance at level P ≤ .05;
∗∗
significance at level P < .01.
Detailed analysis of measurements taken under EO conditions, the results of which are presented in Table 4, confirmed the significant main effect of “Group” factor (F = 6.91, P < .01), as well as the main effect of “PRE–POST factor (F = 14.06, P < .01). In contrast, neither the significant interaction effect (F = 0.20, P = .66) nor significant differences between groups E and C (F = 0.59, P = .45) were observed under EC conditions. However, the significant main effect of “PRE–POST” (F = 8.40, P < .01) was documented. Consequently, there was a statistically significant difference between measurements taken prior to and after sensorimotor exercise. Statistical analysis of SACOP under EO conditions (Figure 4) revealed that group E, i.e., visually impaired women, was characterized by higher values of this parameter as compared to group C (P ≤ .05), both on measurement taken prior to (PRE) and after (POST) completing the exercise on stability trainers. In contrast, during the measurement taken under the EC condition (Figure 4), a slight decrease in SACOP was observed in group E, whereas the significant increase in this parameter (P ≤ .05), by 1.32 ± 3.38 cm2 , was documented in group C. This direction of changes was analogous, as in the case of previously discussed parameters; thus, confirming the role of visual and proprioceptive factors in defining the level of body balance.
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The Effect of Sensorimotor Training on Postural Stability EO
5,0
*
4,0 3,5 3,0
3,38 ± 2,69 3,11 ± 1,99
2,5 2,0
4,5
*
2,33 ± 1,69 2,05 ± 1,32
4,0 3,5 3,0 2,5 2,0
3,55 ± 3,22 3,22 ± 2,66
3,01 ± 2,24 *
2,23 ± 1,55
1,5
1,5 1,0
SACOP [cm2]
SACOP [cm2]
4,5
EC
5,0
PRE
POST
1,0
PRE
POST
Group E
Group C
Group E
Group C
FIGURE 4 Results of ANOVA, mean values, and standard deviations of COP sway area (SACOP ) for the two groups (E—experimental group and C—control group) in two conditions (PRE—pre-exercises condition, POST—postexercises conditions). EO (eyes open) and EC (eyes closed). ∗
A significant group and pre–post condition interaction (P ≤ .05).
TABLE 5 ANOVA Results for Interaction Effect and Between “Group” and “PRE–POST” Factor Effects of COP Sway Area (SACOP ) in Measurements with EO (Eyes Open) and EC (Eyes Closed) Conditions SACOP EO EC ∗
Interaction Effect(1.58) (P)
Factor “Group” F(1.58) (P)
Factor “PRE-POST” F(1.58) (P)
0.01 (0.99)ns 3.44 (0.07)ns
6.39 (0.01)∗∗ 0.20 (0.65)ns
0.93 (0.34)ns 1.84 (0.18)ns
Significance at level P ≤ .05;
∗∗
significance at level P < 0. 1.
Furthermore, the statistically significant main effect of “Group” factor (F = 6.39, P < .01) on measurement taken with eyes open was documented (Table 5). The remaining changes in postural parameters proved statistically nonsignificant.
DISCUSSION AND CONCLUSION The aim of this study was to analyze the effect of sensorimotor training on the postural stability of visually impaired women over 50 years of age. We analyzed the changes that resulted from short-term exposure to destabilizing factors associated with sensorimotor exercise with Thera-Band stability trainers. The study aimed at enhancing the understanding of the process of controlling and maintaining stable posture through a detailed analysis of the determinants of postural stability. Our study sought to elucidate the relationship between postural stability, visual control, and the capacity of the proprioceptive system of the lower limbs. Perhaps understanding the complexity of the mechanisms underlying this process may prove helpful in
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improving the quality of life and promoting reduced falling risk in a group of individuals with visual impairment. Measurements taken with a posturographic system enabled us to analyze the ranges of COP displacement. It is widely believed that the higher range of COP displacement during free standing manifests a reduced level of stability (Judge, Lindsey, Underwood, & Winsemius, 1993; Lord, McLean, & Stathers, 1992). Moreover, the relationship between stable posture and age must be emphasized. It was revealed that progressive aging is associated with degenerative changes within various components of the system of balance control (Lord & Menz, 2000). Our study revealed that in both groups the exercise with stability trainers was reflected by a slight increase in AP, ML, VAVG , and SACOP values determined under static conditions with eyes open. According to Winter (1995), the increase in these parameters can be associated with an independent control of the range of swaying in the sagittal and horizontal plane. VAVG was the only parameter with significant differences between PRE and POST measurements in both groups (E and C). These findings suggest that sensorimotor training has an influence on decreasing postural stability. Detailed analysis conducted in group E revealed markedly higher postexercise values of such posturographic parameters as ML, VAVG , and SACOP . According to Mitchell, Collins, Luca, Burrows, and Lipsitz (1995), increased range of sway in the ML plane is associated with the increased risk of loss of balance and predisposes to falling. An increase in the aforementioned parameters, observed in visually impaired women as compared to the controls, can result from visual deficits. ´ Previous studies (Stemplewski, Maciaszek, Salamon, Tomczak, & Osinski, 2012) revealed that in static examination under EO conditions older individuals are characterized by lower values of posturographic parameters and thus seemingly better postural stability than younger subjects. This paradoxical phenomenon of increased values of COP parameters observed in our study could result from activation of compensatory mechanisms and hence suggest improved body balance in group E participants. Numerous previous studies documented that blind individuals are characterized by a lower level of postural stability, manifested by increased area of COP swaying in coronal and sagittal planes (Blomqvist & Rehn, 2007; Easton, Greene, Dizio, & Lackner, 1998; Schmid, Nardone, De Nunzio, Schmid, & Schieppati, 2007; Sforza et al., 2000). According to Rauschecker (1995) and Schmid et al. (2007), greater COP sways result from the lack of interaction between visual stimuli and motor behaviors. Our findings led us to the conclusion that during the static examination with eyes opened, the experimental group of visually impaired women exhibited a larger range of maximal COP displacement than the control group of women without visual dysfunction; this is reflected by a higher level of postural instability. Vision has the strongest impact on the range of anterior–posterior sway, and the deprivation of visual information is reflected by marked disorders
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of balance. Under such conditions, an immediate increase in the range of COP swaying occurs in individuals without visual impairment (Schieppati, Tacchini, Nardone, Tarantola, & Corna, 1999; Schmid et al., 2007; Sforza et al., 2000). Decreased values of AP, ML, and SACOP were observed during the closed eye measurement in group E; these findings should be interpreted as an increase in postural stability. The application of sensorimotor training was reflected by the activation of compensatory processes in the other systems of balance control. The deprivation of visual stimulation, associated with closing the eyes, resulted in the improvement of postural stability along with the decreased values of baseline characteristics. After completing sensorimotor exercises, a decrease in the amplitude of COP swaying in AP and ML planes, as well as in SACOP, was observed in visually impaired women. Furthermore, after completing the exercise on unstable ground, the values of COP sway in both planes documented in the group of visually impaired women were markedly lower than in the individuals without visual impairment. A reduction in postural stability was documented in the control group C as manifested by considerable increase in all studied parameters: AP, ML, VAVG , and SACOP . As a result of sensorimotor training, group E, composed of visually impaired women, showed a lower range of maximal COP displacement and higher level of postural stability during closed-eye measurement as compared to women without visual dysfunction. Moreover, this study revealed a different effect of visual information on the level of postural stability during measurements taken with open and closed eyes. In the case of visually impaired women, abolishing visual stimulation and implementing exercising on unstable ground was reflected by a higher level of postural stability and compensation of negative influence of visual impairment resulting from extremely effective involvement of other senses. Detailed analysis revealed reduced swaying in the horizontal plane during closed-eye measurement in the control group. These findings can be explained by the fact that identifying lateral movement of the body is easier for the sensimotor system than for the visual system and vestibular organ (Day, Streiger, Thompson, & Marsden, 1993). It is probably the sensorimotor system that is mostly responsible for compensatory function in visually impaired individuals (Capicikova et al., 2006; Sforza et al., 2000). Gravelle et al. (2002) and Collins et al. (2003) observed that greater sways lead to more intense perception of information from the sensorimotor system, consequently improving body stability. Häkkinen et al. (2006) expressed a similar opinion and suggested that to maintain stable posture blind individuals rely on the sensorimotor system to a greater extent than healthy people, who use visual information for this purpose. Patel et al. (2008) highlighted the changes in postural stability induced by visual and sensorimotor destabilizing factors. Our study, involving static measurement, enabled us to conclude that exercise on unstable ground improves postural stability under the open-eyes condition of women without visual dysfunction to a
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greater extent than in those with visual impairment. Previously, other authors (Hosseinimer & Norastech 2010; M˛etel, 2003) postulated the implementation of sensorimotor training programs, suggesting that they can significantly improve both static and dynamic balance of the body. Our findings indicate that women with visual dysfunction can be characterized by varying characteristics of postural stability. Additionally, we confirmed our initial hypothesis according to which the experimental factor, namely sensorimotor training, has a positive influence on analyzed parameters of postural stability, being an effective method of improving postural stability in visually impaired women over 50 years of age. The results of our study can be an important source of information during the planning of compensatory strategies. It should be remembered, however, that our results originate solely from measurements taken under laboratory conditions. In particular, we did not analyze the long-term effect of such an approach within the entire framework of the rehabilitation process of individuals with visual dysfunction, or from the point of view of reducing the risk of falls under natural conditions.
ACKNOWLEDGMENTS The research was conducted by the permission of the Institutional Review Board at Poznan University of Medical Sciences, 10 Fredry Str., 61701 Poznan´ , Poland, number 305/11 from June 16, 2011.
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